Microelectromechanical microphones typically operate in an audible band of frequencies, and also can operate at ultrasonic frequencies. Analog microelectromechanical microphones can include an electro-acoustic sensor that can convert acoustic signals into an electrical signal, and an amplifier that can amplify the electrical signal. Thus, to permit detection of an ultrasonic signal in an analog microelectromechanical microphone, it can suffice that the electro-acoustic sensor, the amplifier, and an acoustic channel of the analog microelectromechanical microphone have a bandwidth extending into ultrasonic frequencies.
In contrast, digital microelectromechanical microphones include an analog-to-digital (A/D) converter that can convert an analog electric signal into a digital signal. The A/D converter can introduce quantization noise into the digital signal through a noise shaping process in which an amount of quantization in the signal band can be mitigated by pushing the low-frequency noise to high frequencies. As such, in the presence of an ultrasonic signal, a noise shaping range of a digital microelectromechanical microphone may be required to extend to frequencies significantly higher than the audible band of frequencies. Therefore, conventional digital microelectromechanical microphones typically increase a clock frequency of the A/D converter and, optionally, another clock frequency of a device that can format output digital signals. Such an approach can be inefficient in terms of noise shaping and can result in high power consumption because ultrasonic signals are usually narrow-band and, therefore, a large portion of the increase in clock frequency leveraged for noise quantization is not applied to frequencies that carry meaningful information. Further, when a maximum available clock frequency in the circuitry associated with the digital microelectromechanical microphone is limited, signal-to-noise ratio can significantly degrade for high-frequency ultrasonic signals.